There exist a number of known techniques for sensory threshold measurement in general and thermal threshold measurement in particular. These are described, inter alia in the following publications:
Goran A. Jamal et al "An Improved Automated Method for the Measurement of Thermal Thresholds. 1. Normal Subjects", Journal of Neurology, Neurosurgery and Psychiatry 1985; 48:354-360; PA1 Clare J. Fowler et al "A Portable System for Measuring Cutaneous Thresholds for Warming and Cooling", Journal of Neurology, Neurosurgery and Psychiatry 1987; 50:1211-1215; PA1 Dan Ziegler et al "Assessment of Small and Large Fiber Function in Long-term Type 1 (insulin-dependent) Diabetic Patients With and Without Painful Neuropathy" Pain, 34(1988) 1-10; PA1 Claus D. Hilz et al "Thermal Discrimination Thresholds: A Comparison of Different Methods", Acta Neurol Scand 1990:81:533-540; PA1 David Yarnitsky et al "Studies of Heat Pain Sensation in Man: Perception Thresholds, Rate of Stimulus Rise and Reaction Time", Pain, 40(1990) 85-91.